I referenced this commits rack/rack@bcf2698

Currently, sinatra drops response body when status code is 205. but, I think it should be able to choice (b).

b)
indicate a zero-length payload for the response by including a
Transfer-Encoding header field with a value of chunked and a message
body consisting of a single chunk of zero-length

Older RFC 2616 text is published at 1990, RFC7231 is published at 2014, so this implementation references RFC2616 probably, I propose 205 remove from DROP_BODY_RESPONSES constants.

what do you think?